Detailing the addresses, maps and logos of Swedish businesses, the websites called for their readers to boycott these firms and "take revenge" on Sweden for the publication of a controversial cartoon by artist Las Vilks.
SAS, H&M, Alfa Laval, TV 4 and Arla were among the companies listed, according to SVT news programme Rapport, which based its report on a study carried out by the Washington-based SITE Institute (the Search for International Terror Entities).
But Scandinavian dairy company Arla, whose goods were boycotted in the Middle East following Denmark's recent caricature row, said it was not aware of any new threats.
"We have not received any indications of a threat," said Tobias Wåhlén, spokesman for Arla Sweden.
H&M on the other hand said it had been kept up to date with developments.
"We received information about it during the afternoon and need to discuss it internally first," said spokeswoman Andrea Roos.
Lars Vilks took part on Tuesday evening in a seminar in Stockholm organized by the Council of Ex-Muslims of Sweden and the Swedish Humanist Association.
Vilks reminded his audience that the drawing had been meant as a provocation. The art and culture communities in Sweden repeatedly criticize the United States and Israel, he said, whereas Muslim countries are rarely even questioned. The caricature of Muhammad as a 'roundabout dog' was his way of "testing the limits" of art.
"I suppose one could say that from that perspective I have been entirely successful," said Vilks.